Breather system for sealed storage structure

ABSTRACT

A sealed storage structure such as a silo having a breather system including a flexible breather bag or equivalent pressurebalancing member. To increase the pressure-balancing capacity of the breather system, a gas cooler assembly is provided. Conduit members connect the cooler assembly to the interior of the silo and to a blower unit to provide a closed gas recirculation path. The cooler and blower are controlled by a thermostat switch within the silo, which switch is set to initiate the recirculation operation at a predetermined maximum temperature and to similarly terminate operation at a predetermined minimum temperature.

3,426,669 2/1969 Peterschmidt................

Inventors Frank D. Hamerski;

Vern D. Overbye, both of Milwaukee. Wis. 817,776

FOREIGN PATENTS 9/1958 Great Britain...

Primary Examiner-William J. Wye

[22] Filed Apr. 21,1969

[45] Patented June 1,1971

[73] A i A. 0. s i h Corporation Att0mey-Andrus, Sceales, Starke &Sawall Milwaukee, Wis.

ABSTRACT: A sealed storage structure such as a silo having a breathersystem including a flexiblebreather bag or equivalent pressure-balancingmember. To increase the pressure-balanc- 3 N 2 E 6 G A R O T S D E L A ES R 0 n T m w S M u w m Ru E flT m TCmL nmc s BS4U 4 U U 5 .m e m m d ma e a m V w m w D.

ing capacity of the breather system, a gas c provided. Conduit membersconnect the cooler assembl the interior of the silo and to a blower unitto gas recirculation path. The cooler and blower are controlled by athermostat switch within the silo, which switch is set to initiate therecirculation operation at a predetermined max- UNlTED STATES PATENTSimum temperature and to similarly terminate operation at a 2,643,6026/1953 Martin............ 6.

98/54 predetermined minimum temperatur PATENTED JUN 1 I97! Jmm'lors v9.filamersh ddbmqys BREATH-HER SYSTEM FOR SEALED STORAGE STRUCTURE Thisinvention relates to generally sealed storage structures andparticularly to breathing means for such structures.

Storage structures such as silos are often constructed to be generallyairtight because of spoilage caused by air coming in contact with thestored materials. Sealed silos, however, experience problems withpressure differentials arising between the interior of such structuresand the ambient. These pressure differentials arise because of gasesbeing generated by the stored material, variations due to ambienttemperature, normal atmospheric pressure changes, and absorption ofsolar heat energy by the silo with the resultant heat transfer to gaseswithin the silo. The situation is undesirable, since too great apressure differential across the walls of a silo can cause destructivestresses in the walls. At the same time it is prohibitively expensive toconstruct structures with wall thickness capable of withstanding themore extreme stresses which could possibly arise.

What is generally done, therefore, is to provide the sealed silo with arelief valve which operates to allow passage of gas from the highpressure side of the wall to the low pressure side when predeterminedmaximum differentials are reached. This method of pressure balancingwill at times allow air into the silo and thus detract from the airtightnature of the unit. Because of the above considerations, the reliefvalve is set to provide a measure of pressure balancing only when themore extreme pressure differentials occur.

To provide a sealed silo with pressure-balancing means, which isoperable within the maximum limits determined by the pressure reliefvalve, breather systems have been developed. The breather system maytake the form of a breather bag installed within the space at the top ofthe silo. The bag has its interior exposed to atmospheric pressure whilethe bags exterior surface is exposed to the pressure in the silo. Byexpanding and contracting in response to differences in the twopressures, the bag tends to erase the pressure differential and thepressure balancing is accomplished without allowing extraneous air intocontact with the stored material.

It has been found that the conventional breather bag and relief valveare capable of balancing pressures under all but extreme conditions.Greater breathing capacity to balance extreme pressure differentials canbe derived by increasing the size or number of breather bags but thismethod of increasing the capacity of the breather system willcorrespondingly reduce the volume available for storage.

In experimenting with silos having breather systems of given capacity,it has been found that extreme pressure differentials can occur. Onemajor cause of extreme differentials was found to be the absorption ofsolar energy by the roof and walls of a silo. It was determined that thegas within the silo reached considerably higher temperatures than theoutside air when being warmed by the sunlight.

The breather bag, being located within the silo, itself absorbs some ofthe solar energy. Thus, the gas within the bag will also tend to be at ahigher temperature than the outside atmosphere and the bag will tend tocontract more slowly than normal, thereby reducing its capacity tobalance the pressure.

Also it was found that a breather bag system has reduced effectivenessto balance pressure differentials which occur beyond a certaintemperature within the silo. Further experimentation has shown that thiscertain silo temperature could be predicted on the basis of dailytemperature variations which are common to a geographical region. Thistemperature was found to be somewhat dependent on the region in whichthe silo was situated and the pattern of temperature variations over theperiod of a day which are commonly experienced in that region. Ofcourse, the solar absorption characteristics of the silo structure werefound to affect the determinations as well.

Other conditions of the atmosphere also tend to create situations whichreduce the effectiveness of the breather system. For instance, when on ahot, sunny day a sudden rainstorm would occur, initially the temperatureof the silo would rise will above the ambient temperature and wouldremain high until falling rain rapidly cools the silo surfaces andsurrounding ambient. The pressure differentials resulting from such acooldown could be of a high magnitude.

The present invention is directed to a structure for increasing thepressurebalancing capacity of the breather system of a sealed storagestructure or silo. According to the invention, chilled gas is suppliedto the silo at times when the tempera ture would be expected to createan extreme pressure differential. The system operates to maintain theconditions within the silo within the range of proper operation ofconventional breather systems. Thus, the pressure balancing is providedby the conventional breather assembly and the invention provides theassurance that extreme conditions will be avoided.

More specifically, the apparatus of the invention includes a coolingunit for cooling gases which are supplied from the storage structure bya conduit and returned to the structure by a second conduit. A blowerunit is connected in one of the conduits and serves to circulate the gaswithin the closed system.

The recirculation-cooling assembly does not operate except at times whenthe certain predetermined temperature is reached. A control unit isprogrammed to actuate the recirculation-cooling unit when a givenmaximum temperature is reached in the storage structure. This givenmaximum temperature is determined on the basis of experience withconditions in the geographical region as they effect a storage structurehaving given solar energy absorption characteristics. Therecirculation-cooling system is programmed to shut off at a silotemperature at which it could be expected the extreme conditions will nolonger occur.

By cooling the gas in the storage structure after the given maximumtemperature has been reached, extreme pressure differentials which arebeyond the capacity of the breather system are avoided and the pressuredifferentials are maintained within the range of proper operation of thebreather system. This permits a smaller sized breather bag to beemployed and thus increases the volume available for storage in thesilo.

Other objects and advantages will occur in the course of the followingdescription:

The drawing illustrates the embodiment of the invention storage mostpreferred by the inventors: diarammatically.

The FIGURE is a side view of the storage structure with part broken awayand portions of the structure shown diagrammatically.

The drawings illustrate a sealed storage structure or silo 1, which isadapted to contain a stored material 2. The silo 1 is supported on afoundation 3 and includes a generally cylindrical wall 4 having an opentop which is enclosed by roof 5. An unloader unit 6 is located in thebottom of the silo and is of a type commonly used, such as thatdisclosed in Tiedmann U.S. Pat. No. 2,635,770. Unloader unit 6 serves todislodge the stored material 2 and to convey the materially to aradially extending trough 7 formed in the foundation 3. The material isconveyed through the trough by a conveying unit 8 and is discharged tothe exterior through a door formed in the end of the housing 9 whichforms an extension of trough 7.

The drawings show a conventional breather assembly associated with thesilo 1 which includes a breather bag 10 suspended from the roof 5 andadapted to expand and contract in the usual manner within the headspacell of the silo. The interior of the bag 10 is exposed to the atmospherethrough the neck 12' secured within an opening in the roof 5, while theexterior of the bag is exposed to the pressure of the gas within thesilo. The bag 10 will expand in headspace 11 in response to a negativepressure differential between the interior of the silo and theatmosphere, and conversely, it will contract in response to positivesilo pressure, thereby serving to equalize silo and ambient pressures.

The breather system also includes a relief valve 13 connected in anopening in the roof 5. Valve 13 is set to allow air to flow intoheadspace 11 when the ambient pressure exceeds the silo pressure by apredetermined value, and conversely, allows gas to flow outwardly whenthe silo pressure exceeds the pressure of the ambient by a predeterminedvalue. The relief valve 13 thus acts to supplement the operation ofthebreather bag 10 when more rapid pressure balancing is required.

To cooperate with the breather system, and to provide a further marginfor more extreme conditions, the invention includes a gas recirculationand cooling system which serves to cool and dehumidify the gas containedwithin the silo. The recirculation and cooling system includes a gascooling unit 14, a blower 15, a conduit 16 and a second conduit 17 whichin conjunction with the interior of the silo, comprise a closed gascirculation system.

The gas cooling unit 14 may be any commercially available refrigeratingunit which is adaptable for cooling gases supplied at moderate to highvolume rates. The cooling unit 14 includes a condensate trap drain 18for collecting and removing condensate from the gas being cooled withinthe unit 14. The gas returned to the silo 1 through conduit 17 is thus,dried as well as cooled.

The inlet of cooling unit 14 is connected to the lower end of silo l byconduit 16 which extends through the foundation 3 adjacent the trough 7toward the center of the silo. The inner end of conduit 16 communicateswith the central portion of trough 7. A screen 19 is disposed over theopen end of conduit 16 is order to keep dislodged stored material 2 fromentering the circulation system. If lower power requirements are desiredfor blower l5, conduit 16 could be connected into the top of the silo,so that the cooled gas would not have to be impelled through the storedmaterial. As well, this system would permit the use of less cooled gasto obtain the same temperature in headspace 11.

Blower 15 is connected in conduit 17 to the exhaust end of cooling unit14 and can be any commercially available variety which can circulate gasat moderate to high volume rates. conduit 17 is in turn, connected tothe headspace 11 of the silo 1. With stored materials, the gas will passthrough the stored material 2 from top to bottom at high enough rates soas to make recirculation as described above feasible.

The recirculation-cooling assembly does not operate continuously. Toprogram the system s operation, a control unit is provided and includesa temperature responsive actuator, such as a thermostat 20, disposed inthe headspace 11 and connected through a suitable electrical controlcircuit to the blower l and cooling unit 14. The thermostat 20 isdesigned to initiate recirculation and cooling at a predeterminedmaximum silo temperature, and to terminate the operation after theheadspace 11 has been cooled to a second predetermined minimumtemperature.

The system control may embody a pressure responsive actuator responsiveto internal silo pressure, in addition to the previously mentionedthermostat. The function of the presureresponsive actuator would be tooverride the primary thermostat control and initiate startup of therecirculation-cooling system when preselected high pressure in the silois exceeded and to prevent operation of the recirculation-cooling systemwhen silo pressure is less than a preselected low pressure setting.

In the manner of the invention, the conventional breather assembly,meaning the bag and the relief valve 13, is continuously operating toequalize pressure differentials in the silo. At a silo temperaturecorresponding to the value at which the conventional breather assemblyapproaches its designed capacity, or the predetermined maximumtemperature, the contacts of thermostat 20 are closed to close thecircuit to the blower and the cooler 14 to start their operation. Gasthen begins to circulate from silo 1 through the conduit 16 to thecooling unit where the gas is cooled and excess water vapor iscondensed. Blower 15 delivers the cooled and dehumidified gas to theheadspace 11 through conduit 17. The operation continues until thethermostat senses the shutoff temperature in the silo and signals theblower 15 and the cooler 14 to terminate operation. In some units, itmay be desired to employ more complicated control sequences, such as onewhich interposes a time delay between the cooler shutoff and blowershutoff.

Although the maximum temperature and shutoff temperature are dependenton such factors as color of the silo roof 5, the amount of storedmaterial 2 contained in the silo l, and the geographical region of usefor the system, it has been found that temperature values ranging fromto 1 10 F. and preferably from to F. for the maximum temperature givereasonable assurance that the conventional breather system will beoperating within its range of capability. The shutoff temperature shouldbe from 20 to 30 F. below the maximum temperature, and preferably from20 to 25 F. below the maximum temperature, so that the system does notcontinually fluctuate through on-off cycles.

Various modes of carrying out the invention are contemplated as beingwithin the scope of the following claims particularly pointing out anddistinctly claiming the subject matter which is regarded as theinvention.

We claim:

1. In a storage unit having a generally sealed storage structure forstoring a perishable material, the storage structure having a headspaceand a breather system operating in fluid communication with theheadspace; a gas-cooling system comprising:

a gas-cooling unit;

a first conduit connecting the gas-coolin g unit to the storagestructure,

a second conduit connecting the cooling unit to the headspace of thestorage structure,

gas-recirculating means for conveying gas through the first conduitmeans from the structure to the gas-cooling unit and for returning gasdischarged from said gas-cooling unit through the second conduit meansto the headspace; and

a temperature-responsive control means disposed in the headspace foractuating said gas-cooling unit and gasrecirculating means in responseto the temperature in the headspace reaching a first selected value inthe range of 90 F. to 1 10 F., and for terminating the operation of saidgas-cooling unit and gas-recirculating means in response to a secondtemperature in the headspace reaching a second selected value in therange of 20 F. to 30 F. less than said first selected value, whereby theoperation of the breather system is supplemented in high temperatureconditions.

2. A method of balancing the pressure in the interior of a generallysealed storage structure having a headspace and a flexible breather unitoperating in fluid communication with the headspace, comprising thesteps of:

cooling the headspace when the temperature in the headspace reaches afirst selected value in the range of 90 F. to 1 10 F and terminatingTerminating the cooling of the headspace when the temperature in theheadspace reaches a second selected value in the range of 20 F. to 30 F.less than said first selected value.

3. A method of balancing the pressure differentials between a generallysealed storage structure and the ambient, the storage structure having aheadspace containing a gas and an expandible breather member in saidheadspace; comprising:

continuously operating the expandible breather member to expand andcontract such as to generally equalize the pressure in the headspace andthe ambient; and

maintaining the temperature in the headspace below a predeterminedmaximum value at which the expandible breather member experiencesdecreased effectiveness.

4. The method of claim 3 wherein the temperature is main tained byrecirculating and cooling the gas in the headspace when saidpredetermined maximum value is reached, and terminating therecirculating and cooling when a predetermined lower temperature isreached; said predetermined maximum value being in the range of 90 F. to1 10 F., and said predetermined lower temperature being in the range of20 F. to 30 F. less than said predetennined maximum value.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,58l,5l4 Dated June 1, 1971.

Inventor(s) Frank D. Hammerski and Vern D. Overbye It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 2, line 45 cancel "storage" and substitute therefor--presently---, column 2, line 45 cancel "diarammatically" column 4,line 53 cancel "Terminating", second occurrence.

Signed and sealed this th day of January 1972.

( SEAL Attest:

EDWARD M.FLETCHEH, JR. ROBERT GOTTSCHALK Attesting Officer ActingCommissioner of Patents FORM PO'1O50UO'59) USCOMM-DC 6D376-P69 9 U 5GOVERNMENT PRINTING OFFICE: 1969 O355-334

1. In a storage unit having a generally sealed storage structure forstoring a perishable material, the storage structure having a headspaceand a breather system operating in fluid communication with theheadspace; a gas-cooling system comprising: a gas-cooling unit; a firstconduit connecting the gas-cooling unit to the storage structure, asecond conduit connecting the cooling unit to the headspace of thestorage structure, gas-recirculating means for conveying gas through thefirst conduit means from the structure to the gas-cooling unit and forreturning gas discharged from said gas-cooling unit through the secondconduit means to the headspace; and a temperature-responsive controlmeans disposed in the headspace for actuating said gas-cooling unit andgas-recirculating means in response to the temperature in the headspacereaching a first selected value in the range of 90* F. to 110* F., andfor terminating the operation of said gas-cooling unit andgasrecirculating means in response to a second temperature in theheadspace reaching a second selected value in the range of 20* F. to 30*F. less than said first selected value, whereby the operation of thebreather system is supplemented in high temperature conditions.
 2. Amethod of balancing the pressure in the interior of a generally sealedstorage structure having a headspace and a flexible breather unitoperating in fluid communication with the headspace, comprising thesteps of: cooling the headspace when the temperature in the headspacereaches a first selected value in the range of 90* F. to 110* F.; andterminating Terminating the cooling of the headspace when thetemperature in the headspace reaches a second selected value in therange of 20* F. to 30* F. less than said first selected value.
 3. Amethod of balancing the pressure differentials between a generallysealed storage structure and the ambient, the storage structure having aheadspace containing a gas and an expandible breather member in saidheadspace; comprising: continuously operating the expandible breathermember to expand and contract such as to generally equalize the pressurein the headspace and the ambient; and maintaining the temperature in theheadspace below a predetermined maximum value at which the expandiblebreather member experiences decreased effectiveness.
 4. The method ofclaim 3 wherein the temperature is maintained by recirculating andcooling the gas in the headspace when said predetermined maximum valueis reached, and terminating the recirculating and cooling when apredetermined lower temperature is reached; said predetermined maximumvalue being in the range of 90* F. to 110* F., and said predeterminedlower temperature being in the range of 20* F. to 30* F. less than saidpredetermined maximum value.